1. Field of the Invention
The present invention relates to an organic electroluminescent (EL) element that includes a silver thin film electrode and has high luminous efficiency and to a light-emitting apparatus that includes the organic EL element.
2. Description of the Related Art
An organic EL element includes a first electrode, a second electrode, and an organic compound layer disposed between the two electrodes. Light produced in a light-emitting layer in the organic compound layer is extracted from the first electrode or the second electrode (a light extraction electrode). It has been proposed that a silver thin film is used as the light extraction electrode. Silver has high electrical conductivity and high transmittance in the visible light region.
However, a silver thin film having a thickness of 20 nm or less is generally a discontinuous film, having not only a small electric conductivity but also low transmittance in the visible light region because of absorption resulting from local surface plasmon resonance. In order to prevent the absorption due to local surface plasmon resonance of the silver thin film, Japanese Patent Laid-Open No. 2008-171637 discloses an organic EL element that includes an electrode formed of a layered transparent electroconductive film. The layered transparent electroconductive film is composed of an underlying layer formed of a metal other than silver and a silver thin film layer formed of silver or a silver alloy. The metal other than silver is preferably selected from the group consisting of gold, aluminum, copper, indium, tin, and zinc.
As a result of diligent research, however, the present inventors found that the structure of the layered transparent electroconductive film according to Japanese Patent Laid-Open No. 2008-171637 could not sufficiently prevent absorption due to local surface plasmon resonance.